WASHINGTON — Sen. John Kerry, President Barack Obama's pick for secretary of state, is a familiar face to the world leaders vital to American interests.

The son of a diplomat and Obama's unofficial envoy, Kerry spent hours walking around the palace in Kabul persuading Afghanistan President Hamid Karzai to agree to a runoff election in fall 2009. The relationship will be crucial in the coming months as the administration draws down U.S. forces after more than a decade of war.

In Pakistan, Kerry helped quell the anger after the U.S. incursion into the country to kill Osama bin Laden in May 2011. The uneasy ties between Washington and Islamabad will be a priority for Kerry at the State Department.

"He knows most of the world leaders," said Sen. Lindsey Graham, R-S.C. "So when he goes into a country he will be a known quantity."

The five-term Massachusetts senator has spent his entire congressional career on the Foreign Relations Committee, the last six as chairman. He has traveled extensively both as intrepid lawmaker and administration emissary.

Fulfilling a Kerry dream, Obama on Friday tapped the 69-year-old lawmaker, a decorated Vietnam War veteran and 2004 Democratic presidential nominee, to replace Secretary of State Hillary Rodham Clinton for the top job at Foggy Bottom.

"I think it's fair to say that few individuals know as many presidents and prime ministers, or grasp our foreign policies as firmly as John Kerry," Obama said in making the announcement. "And this makes him a perfect choice to guide American diplomacy in the years ahead."

Kerry is expected to sail to confirmation, with both Republicans and Democrats praising the nomination. His friend, Sen. John McCain, R-Ariz., jokingly referred to him as "Mr. Secretary" earlier this month, a remarkable turn as just eight years ago Republicans ridiculed Kerry as a wind-surfing, elitist flip-flopper in his bid for the White House.

While Kerry has tamped down diplomatic fires for Obama, he has stepped ahead of the administration on a handful of crises. He joined McCain as an early proponent of a more aggressive policy toward Libya, pushing for using military forces to impose a "no-fly zone" over Libya as Moammar Gadhafi's forces killed rebels and citizens.

He was one of the early voices calling for Egyptian President Hosni Mubarak to step down as the revolution roiled the nation last year.

That independent voice may be tempered once he takes over as the administration's top diplomat.

"He's going to find what it's like to be part of an administration," said Sen. Richard Burr, R-N.C. "John's going to adapt to this well. I think he spent a lot of his time grooming to be a good secretary of state. ... I don't see any downside to this nomination."

During his tenure, Kerry has pushed for reducing the number of nuclear weapons, shepherding a U.S.-Russia treaty through the Senate in December 2010, and has cast climate change as a national security threat, joining forces with Republicans on legislation that faced too many obstacles to win congressional passage.

He has led delegations to Syria and met a few times with President Bashar Assad, now a pariah in U.S. eyes after months of civil war and bloodshed as the government looks to put down a people's rebellion. Figuring out an end-game for the Middle East country would demand all of Kerry's skills.

The selection of Kerry closes a political circle with Obama. In 2004, it was White House hopeful Kerry who asked a largely unknown Illinois state senator to deliver the keynote address at the Democratic convention in Boston, handing the national stage to Obama. Kerry lost that election to President George W. Bush. Four years later, Obama was the White House hopeful who succeeded where Kerry had failed.

Throughout this past election year, Kerry skewered Obama's Republican rival, Mitt Romney, at nearly every opportunity and was a vocal booster for the president's re-election. Kerry memorably told delegates at the Democratic National Convention in August: "Ask Osama bin Laden if he's better off now than he was four years ago."

Kerry and McCain, defeated presidential candidates who returned to the Senate, have joined forces repeatedly during the past few decades. In July 1995, the two decorated Vietnam War veterans provided political cover to President Bill Clinton when he normalized U.S. relations with Vietnam. Clinton had been dogged by questions about his lack of military service.

Kerry, the Yale graduate who enlisted in the Navy, was an appealing presidential nominee in 2004 for his Vietnam War service. Three years after the Sept. 11 terror attacks, national security credentials were critical against Bush.

But Kerry was pounded by the Swiftboat Veterans for Truth, a group that made unsubstantiated claims challenging Kerry's war record of a Silver Star, a Bronze Star for combat valor and three Purple Hearts. His candidacy also was dogged by his anti-war stance in April 1971 when he testified before the committee he would later chair and famously asked, "How do you ask a man to be the last man to die for a mistake?"

Kerry's move to the State Department will spark yet another special election in Massachusetts — the third Senate contest since a 2010 special election following the death of Sen. Edward M. Kennedy in 2009.

Republican Sen. Scott Brown, who won the 2010 special election but lost last month to Democratic challenger Elizabeth Warren, is seen as a front-runner on the GOP side if he chooses to run again.

Possible Democratic candidates include Reps. Michael Capuano, Edward Markey and Stephen Lynch, and Ted Kennedy Jr., son of the late senator. Gov. Deval Patrick must name an interim senator to serve until the special election. Former Gov. Michael Dukakis and Victoria Kennedy, Edward M. Kennedy's widow, have been suggested as possible interim senators although Patrick hasn't publicly confirmed any names.

Kerry was in Pakistan last year in the midst of a diplomatic crisis after Raymond Davis, a CIA-contracted American spy, was accused of killing two Pakistanis.

Sen. Chris Coons, D-Del., a member of the Foreign Relations Committee, traveled to Pakistan around that time and recalled Kerry's influence.

"I arrived in Islamabad, I think, five days after Ray Davis had been taken into a jail in the Punjab and was at very real risk of being hauled out of the jail and lynched," Coons said. "Sen. Kerry was about to show up and negotiate on behalf of the administration. And it was clear that both the diplomats and the military folks we met with viewed him as a real man of credibility and experience who was likely to contribute meaningfully to those negotiations."

Davis pleaded self-defense. After weeks of wrangling between the U.S. and Pakistan, he was released in exchange for "blood money" paid to the dead men's relatives.

Sen. Bob Menendez, D-N.J., who likely will take over the chairmanship of the Foreign Relations Committee, said the high-level relationships that Kerry "built with world leaders will allow him to step seamlessly into the position and to ensure that there is no decline in U.S. leadership on important global issues during a transition."

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Donna Cassata can be reached on Twitter at http://twitter.com/DonnaCassataAP